program vijos1007;
var
    n,i:longint;
    r,ans:real;
    data:array[1..100,1..2] of real;
begin
    assign(input, '');
    assign(output, '');
    reset(input);
    rewrite(output);

    readln(n,r);
    for i:=1 to n do
        readln(data[i,1],data[i,2]);
    for i:=2 to n do
        ans := ans+sqrt(sqr(data[i,1]-data[i-1,1])+sqr(data[i,2]-data[i-1,2]));
    ans := ans+sqrt(sqr(data[1,1]-data[n,1])+sqr(data[1,2]-data[n,2]));
    ans := ans+2*PI*r;
    writeln(ans:0:2);

    close(input);
    close(output);
end.
